A typical automobile engine starter includes a solenoid that is activated upon closing an ignition switch. As shown in FIG. 1, the solenoid includes two terminals 30a and 30b, a contact disc 28, a contact rod 26, a plunger 24, and windings 22. The contact disc 28 is connected to the contact rod 26 and biased by a return spring 66 away from the terminals 30a and 30b. The plunger 24 is separated from the contact rod 26 across an air gap 29. A rod 52 on the plunger 24 is connected to one end of a shift lever 80. The opposite end of the shift lever 80 is connected to a pinion 82. The pinion 82 is generally in some slideable relationship to the drive shaft 84 of an armature 88.
The operator of an automobile cranks the engine by turning a key or pressing a button that closes an ignition switch (not shown). When the ignition switch is closed and electric current is provided to the solenoid windings 22. Upon excitation of the solenoid, the plunger 24 moves into the body of the solenoid. This causes the shift lever to rotate about its pivot point 81. Rotation of the lever 80 about the pivot point causes the lever to move the pinion 82 linearly in the direction of arrow 86, sliding the pinion towards the engine flywheel ring gear (not shown). Upon reaching the ring gear, the teeth of the pinion 82 mesh with the teeth of the ring gear. Subsequent rotation of the pinion 82 will rotate the ring gear and crank the automobile engine.
As the pinion 82 is forced toward the ring gear, as a result of solenoid plunger movement, the plunger 24 moves linearly in the direction of arrow 87 to reduce a magnetic air gap 31 within the solenoid. Plunger movement toward the terminals brings the plunger into contact with the contact rod 26. As a result of plunger movement, the contact rod 26 and connected contact disc 28 are moved in the direction of the terminals 30a and 30b until the contact disc 28 comes into contact with the terminals 30a and 30b. When the contact disc 28 physically touches the terminals 30a and 30b, an electric circuit is completed which provides cranking current to drive the armature. Energization and subsequent rotation of the armature transmits rotational power to the drive shaft 84 and pinion 82. Rotation of the pinion 82 and ring gear transmits rotational force to a crankshaft (not shown) which causes the automobile engine to rotate as part of the starting cycle.
After the engine has fired, the driver generally releases the key, causing the ignition switch to open, and current is no longer provided to the solenoid windings 22. When the solenoid is no longer excited by electric current, a plunger biasing spring 42 pulls the plunger 24 away from the terminals 30a and 30b and back to its non-excited position. With the plunger 24 no longer abutted against the contact rod 26, the return spring 66 forces the contact disc 28 and contact rod 26 away from the terminals 30a and 30b. 
In the making and breaking of cranking currents there is a partial welding/fusing or co-joining of materials between the contact disc and the terminals. Under most normal circumstances, the return spring 66 maintains enough force to disjoin or mechanically break this partial fusing of materials. However, there exists a potential for fusing strength in excess of the available return spring 66 force. This potential is influenced by many factors relating to overall starting system and application integrity both new and over the life cycle of the vehicle. When the return spring 66 force is exceeded by the fused material strength of the contact to terminals the starter armature will continue to be energized after the operator releases the ignition switch. When this happens, the armature will continue to run even after the vehicle engine has fired and the pinion has disengaged the ring gear. Continuous running of the armature absorbs a great deal of electrical energy from the battery, making less electrical energy available for other automobile systems. If the armature runs for too long, it may completely drain the battery. Furthermore, because the armature is not intended to run for a long period of time, extended running of the armature may cause it to over heat and cease to function. For the foregoing reasons there is a need for a solenoid that significantly reduces the susceptibility of starter failure as a result of contact welding/fusing.
The present invention is directed to an apparatus that satisfies the need for a solenoid that significantly reduces the susceptibility of starter (also referred to herein as a starter motor) to failure as a result of contact welding/fusing. The apparatus comprises a solenoid having a bobbin and a winding for receiving electric current. A plunger is positioned in electromagnetic communication with the winding such that energizing the winding with current will cause the plunger to slide within the bobbin in one direction. A plunger biasing spring causes the plunger to slide in the opposite direction when electric current is removed from the winding.
The plunger includes a center cavity extending axially within the plunger. The center cavity includes a shoulder at one end which defines an axial bore having a smaller diameter than the center cavity. An opposite end of the center cavity is defined by an abutment pin positioned in a slot extending perpendicularly through the center cavity.
An impact device is slideably positioned in the center cavity of the plunger. The impact device is bounded in the center cavity of the plunger by the shoulder and the abutment pin. The impact device is connected to one end of a contact rod which extends in a slideable relationship through the axial bore of the plunger. The opposite end of the contact rod holds a contact. Thus, the impact device is in communication with the contact through the mechanical link of the contact rod. Movement of the impact device in one direction will cause the contact to move in that direction and, likewise, movement of the impact device in the opposite direction will cause the contact to move in that opposite direction. The contact generally moves toward a set of terminals to establish a connection between the contact and terminals or away from the set of terminals to break a connection between the contact and terminals.
When the winding is energized, the pinion moves further into the bobbin. This movement of the plunger causes the abutment pin to contact the impact device and move it toward the terminals. Movement of the impact device toward the terminals also moves the contact and establishes a connection between the contact and the terminals. Removing electric current from the winding will result in the plunger biasing spring causing the plunger to slide within the bobbin in a direction away from the terminals. When the plunger moves in this direction, the shoulder of the plunger slams into the impact device and carries the impact device in the direction of plunger movement. Movement of the impact device away from the terminals pulls the contact rod and contact away from the terminals and forcefully breaks the established connection between the contact and terminals. Because of this forceful separation of the contact from the terminals, the susceptibility of starter failure resulting from contact welding/fusing is significantly reduced. These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims.